1. Technical Field
The present invention relates to a liquid ejecting head that includes a piezoelectric element which has a piezoelectric layer and electrodes for applying a voltage to the piezoelectric layer so as to change the pressure in a pressure generating chamber communicating with a nozzle hole. The invention also relates to a liquid ejecting apparatus and a piezoelectric element.
2. Related Art
A piezoelectric element is used in a liquid ejecting head as a piezoelectric actuator in which two electrodes sandwich a piezoelectric layer formed of a piezoelectric material capable of converting electricity to mechanical work, for example a crystal dielectric material. A typical example of a liquid ejecting head is an ink jet recording head. In an ink jet recording head, a diaphragm constitutes part of a pressure generating chamber that communicates with a nozzle hole through which ink droplets are ejected, and the diaphragm is deformed by a piezoelectric element to pressurize an ink contained in the pressure generating chamber, thereby ejecting ink droplets from the nozzle hole.
Such piezoelectric materials that are used as piezoelectric layers (piezoelectric ceramics) in piezoelectric elements require high piezoelectric properties. As a typical example of one such piezoelectric material, JP-A-2001-223404 describes lead zirconate titanate (piezoelectric zirconate titanate (PZT)).
However, concerns for environmental issues have led to the need for piezoelectric materials containing less or no lead. An example of a lead-free piezoelectric material is BiFeO3 which has a perovskite-type structure represented by ABO3. The letters A and B in ABO3 respectively indicate a 12-coordinate A site and a 6-coordinate B site occupied by oxygen atoms. However, BiFeO3 piezoelectric materials have such low insulating properties that leakage current occurs easily. The high probability of leakage current increases the risk that cracks are caused, in particular when a high voltage is applied to the piezoelectric material. Thus, such piezoelectric materials are not suited for use in liquid ejecting heads. In order for a piezoelectric material to be used in a piezoelectric element, high insulating properties are required such that the leakage current is not more than 1×10−3 A/cm2 at 25 V, which is a typical drive voltage.
The problems described above are encountered not only with the ink jet recording heads but also with other liquid ejecting heads that eject liquid droplets other than ink droplets as well as with piezoelectric elements used in devices other than liquid ejecting heads. Further, the leakage current problem leads to another serious problem that the piezoelectric element consumes more energy when used as a sensor. Low leakage current is also preferable for piezoelectric elements used in piezoelectric sensors, infrared sensors, heat sensitive sensors and pyroelectric sensors that are operated at an applied voltage of 1 V or less.